48 ABSORPTION SPECTRA OF SOLUTIONS. 



The limits of transmission for the first and seventh solutions in A are, 

 respectively, A 5250 and A 5080, the edge forming a line which curves 

 slightly from the first to the fourth strips, then becomes straight. The 

 corresponding limits for B are A 4750 and A 4600, the edge forming a line 

 which is straight from the first to the fifth solutions, then curves slightly 

 towards the seventh, the convex side being towards the shorter wave- 

 lengths. It will be noticed that the edge of the absorption band here is 

 very similar to what we found in the methyl alcohol solutions, the only 

 difference being that here it is located about 400 Angstrom units nearer 

 the red end of the spectrum. 



The absorption in the red apparently obeys Beer's law quite accurately, 

 the edge of the band remaining in practically the same position for the 

 seven solutions of a set. This position for A is at -} 6200, for B at A 6700. 

 The shading in A is noticeable at ^ 5900, in B at A 6400. Here, then, the 

 edge of the band is, on the whole, nearer the violet end of the spectrum by 

 about 250 Angstrom units than was the case in the methyl alcohol solutions. 



COPPER CHLORIDE IN ACETONE BEER'S LAW. (See Plate 34.) 



The concentrations of the solutions used in making the negative for 

 B, beginning with the one whose spectrum is adjacent to the numbered 

 scale, were 0.02, 0.0168, 0.0139, 0.0114, 0.0094, 0.0080, and 0.0066, the 

 corresponding depths of absorbing layer being 8, 9.5, 11.5, 14, 17, 20, and 

 24 mm. For set A the concentrations were varied from 0.008 to 0.0027, 

 the depths of cell being the same as in B. 



The most concentrated solutions were greenish-yellow, from which the 

 color changed gradually to a pale yellow with dilution. 



The exposures were made to the light from the Nernst lamp only, a 

 preliminary trial showing that the entire ultra-violet region was absorbed 

 by a comparatively shallow layer of the most dilute solution. The time 

 of exposure was 1 minutes; the slit having a width of 0.01 cm. as usual. 



There is a region of absorption in the violet which in B first narrows 

 slightly with dilution, then begins to widen, and continues to do so through- 

 out the entire range of concentrations studied. The limit of transmission 

 for the most concentrated solution of set A is at h 4130. In the strip corre- 

 sponding to the third solution it is at h 4100, from which it moves regularly 

 towards the red, reaching ^ 4150 in the seventh strip. 



In the first solution of set A the limit of transmission is at A 3850. It 

 moves towards the red quite regularly with dilution, reaching A 3950 in 

 the strip corresponding to the seventh solution. A shows an absorption 

 band having its center at X 4750. This band, which is about 200 A.U. 

 wide, remains of constant width throughout. In A, though still visible, 

 it is rather faint. Its position is, however, exactly the same as in B. 



In the red, both B and A show transmission as far as X 7400, or to the 

 limit of the sensibility of the plates used. The slight shading in B, how- 

 ever, indicates some absorption in the extreme red, and also points to the 

 conclusion that this absorption increases somewhat with dilution. 



This is the first case we have found where the absorption increases with 

 dilution when the product of concentration and depth of absorbing layer 



